This study was performed to investigate the influence of low crude protein diet (LCP, 13%) and different dietary levels of zinc with or without vitamin D3 on the productive and reproductive performance of Gimmizah chickens during the late laying period. A total number of 280 (245 hens + 35 cocks) Gimmizah chickens aged 52-week were individually weighed and randomly divided into seven treatment groups with five replicates for each during the experimental period (52-64 weeks of age). The birds of the first group were fed the basal diet (15%CP) and served as control. Second one was fed LCP, 13% without any supplementation, whereas the third and fourth groups were fed LCP diet supplemented with zinc (Zn, 50 and 100 mg/kg diet, respectively). The fifth group was fed LCP diet supplemented with vitamin D3 (Vit D3, 2000 IU/kg diet). While, the sixth and seventh groups were fed LCP diet supplemented with Zn (50 mg/kg diet) plus Vit D3 (2000 IU/kg diet), and Zn (100 mg/kg diet) plus Vit D3 (2000 IU/kg diet), respectively. The chickens fed LCP diet had significantly the worst records of egg production, egg mass and feed conversion ratio compared with the control group. While, supplemented LCP diet with Vit D3 or both levels of Zn plus Vit D3 similarly restored the previous mentioned parameters to the level of control group. Specific gravity of eggs, yolk dry matter and yolk index for birds fed LCP diet were significantly decreased compared with control. However, supplemented LCP diet with studied agents significantly improved shell weight, shell thickness, SWUSA and yolk color compared with control. Fertility and hatchability percentages for aged chickens fed LCP diet supplemented with both levels of Zn plus Vit D3 were significantly increased compared with control and LCP diet groups. Birds fed LCP diet supplemented with Vit D3 or both levels of Zn plus Vit D3 had significant improvement for RBCs, Hgb, PCV, WBCs, lymphocyte, phagocytic activity, cholesterol, HDL, LDL, antioxidant status and calcium compared with control and LCP diet groups. Total protein, albumin and globulin for birds fed LCP diet supplemented with 50 mg Zn /kg diet plus Vit D3 did not represent any statistical change compared with control group. In conclusion, supplementing the chickens fed LCP diet (13% CP) during the late stage of laying cycle with Zn (50 mg/kg diet) plus Vit D3 (2000 IU/kg diet) could be a good tool for realizing the best results of productive and reproductive performance besides the best record of economical efficiency.
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